Rotational drive mechanism

ABSTRACT

A photoelectrophoretic imaging system is disclosed wherein complementary images are formed from a photosensitive ink placed between a flat transparent conductive plate and a conductive roller coated with a dielectric material. The flat plate is transparent and a light image is projected to the ink through it. The plate and roller are coupled to a voltage source to establish an electric field between them as required by the photoelectrophoretic process; therefore the complementary images are formed as the roller is moved over the surface of the plate. The roller is propelled past the plate by a hydraulic cylinder having its piston rod coupled to the roller and it is made to rotate at an angular velocity directly related to its linear velocity by a link chain anchored at two ends and looped over a mating sprocket coupled to the roller.

United States Patent 1 Roselli [54] ROTATIONAL DRIVE MECHANISM Frank A. Roselli, Webster, NY. [73] Assignee: Xerox Corporation, Rochester, NY. [22] Filed: July 26, 1971 [21] Appl. No.: 166,287,

[75] Inventor:

Related U.S. Application Data [63] Continuation ofSer. No. 820,756, May 1, 1969,

Primary ExaminerJohn M. Horan Assistant Examiner-Kenneth C. Hutchison Attorney-Paul M. Enlow, James J. Ralabate, Norman E. Schrader and Ronald Zibelli 1 June 5, 1973 57 ABSTRACT A photoelectrophoretic imaging system is disclosed wherein complementary images are formed from a photosensitive ink placed between a flat transparent conductive plate and a conductive roller coated with a dielectric material. The flat plate is transparent and a light image is projected to the ink through it. The plate and roller are coupled to a voltage source to establish an electric field between them as required by the photoelectrophoretic process; therefore the complementary images are formed as the roller is moved over the surface of the plate. The roller is propelled past the plate by a hydraulic cylinder having its piston rod coupled to the roller and it is made to rotate at an angular velocity directly related to its linear velocity by a link chain anchored at two ends and looped over a mating sprocket coupled to the roller.

3 Claims, 3 Drawing Figures ROTATIONAL DRIVE MECHANISM CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation of Ser. No. 820,756, filed May 1, 1969, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to photoelectrophoretic imaging systems of the type wherein a roller electrode is passed over another electrode to form an image from a liquid ink dispersed between the two electrodes. In particular, this invention relates to a novel drive mechanism for establishing a desired relationship between the angular and translational velocities of the roller electrode.

In the photoelectrophoretic imaging process, an image is formed from an imaging suspension or ink which is subjected to an electric field and exposed to activating electromagnetic radiation, i.e., light. The imaging suspension is a non-conductive liquid carrier having suspended therein light sensitive particles which are i believed to bear a net electrical charge while in suspension. The imaging suspension is placed between two electrodes, used to establishthe electric field, and is exposed to a light image through one of the electrodes which is at least partially transparent. According to one theory, particles attracted to the transparent electrode under the influence of the electric field and exposed to exchange with the particles thereby preventing the .par-

ticles from oscillating back and forth between the two electrodes. The electrode allowed to exchange charge with the particles is referred to as an injecting electrode and the electrode coated with the dielectric material to prevent charge exchange is referred to as a blocking electrode. The photoelectrophoretic imaging process is either monochromatic or polyc'hromatic depending upon whether the light sensitive particles within the liquid carrier are responsive to the same or different portions of the light spectrum. A full color system is obtained, for example,'by using cyan, magentaand yellow colored particles which are responsive to red, green and blue light respectively. An extensive 'and detailed description of the photoelectrophoretic process is found in US. Pat. Nos; 3,384,566, 3,384,488, 3,383,993, and 3 ,384,565.

The above identified patents disclose apparatus which includes a conductive roller member preferably coated with a dielectric material, and aflat, transparent conductive plate which serve as the imaging system blocking and injecting electrodes respectively. The roller and plate are coupled to a voltage sourceto establish an electrical field between them'and the ink is placed over the plate and is exposed to a light image. Therefore, as the roller traverses the plate images are formed on the plate'and roller. The quality of an image is affected, at least in part, by therelative velocity between the point on the surface of the roller in contact with the plateand a correspondingpoint on the-plate. If thi's'relative velocity is anything but zero, the roller is rotating too fast or too'slow as compared'to the velocity of the roller across the plate (translational velocwhich does not require adirect coupling cult to avoid this problem if the friction between the roller and plate is relied on to rotate the roller because the ink required by the process to be between the roller' and plate acts asa lubricant which impedes the frictional engagement between them.

The present invention solves the foregoing problem by utilizing a novel drive mechanism that matches the speed of a point on the surface of the roller (surface speed) to the magnitude of the translational velocity of the roller. In the invention, the angular velocity of the roller is made directly dependent upon its translational velocity by utilizing a stationary chain which is anchored at two ends and looped over a sprocket coupled to the roller. As the roller is forced along the length of the chain by an independent drive mechanism it is caused to rotate at an angular velocity related to the translational speed of the roller. By selecting the appropriate pitch diameter for the sprocket the surface speed of. the roller is made substantially equal to the translational speed.

The looped chain is a positive drive. mechanism for rotating the roller which substantially eliminates back lash. This drive mechanism is extremely versatile in that it is capable of being incorporated into diverse machine structures with relative ease because it is not necessary to precisely align the chain relative to the roller or to the path over which it travels. In this regard the present drive mechanism is especially advantageous if the path over which the roller travels is relatively long.

I In addition, because the present drive mechanism is completely separate from the drive mechanism propelling the roller, a wide variety of drive mechanism is available for imparting the translational movement to the roller.

Accordingly, it is an object of this invention to improve photoelectrophoretic imaging systems of the foregoing type by'minimizing the detrimental affects to an image formed during the traversal of one electrode by another. Specifically, is an object of the invention to prevent smearing of an image formed as a roller electrode traverses a plate electrode.

Itis another object of this invention to rotate a translating roller member at an angular velocity that is directly related to the translational velocity of the roller.

A'further object of the invention is to devise a drive mechanism forrotating a translating member that ,permits a wide tolerance range for component alignment yet insures positive rotation of the roller.

Even a further object of this invention is to provide a drive mechanism for rotating a translating member to the drive mechanism jpropelling'the member.

DESCRIPTION OF T HEgDRAWlNG S Otherobjects and features of the invention will be apparent'from the accompanying drawings wherein:

" FIG. 1 is schematic representation of a photoelectro-' phoretic'imaging system utilizing the drive mechanism of the present invention;

FIG. 2 is.a cross-section view of the imaging system shown in FIG. 1 taken along lines 2-2; and

FIG. 3 is an isolated view of the sprocket and roller of FIG. 2 illustrating their relative diameters.

The photoelectrophoretic machine or system shown in the drawings includes the frame 1, the carriage 2; the roller member 3, the transparent conductive flat plate 4, the exposure mechanism 5, the rotational drive mechanism 6 and the translational drive mechanism 7.

The transparent plate 4 is supported by the frame 1 at the position relative to the carriage and roller as shown in the drawings. The particular support structure coupling the transparent plate to the frame is not shown in order to simplify the drawing and thereby clarify the present discussion. The transparent plate serves as the injecting electrode for the photoelectrophoretic process and consists of an optically transparent glass 8 overcoated with a thin optically transparent layer of tin oxide 9. The specific plate described is commercially available under the name NESA glass. The roller 3 serves as the blocking electrode for the photoelectrophoretic process and includes a conductive center core 11 and an outer layer of relatively high dielectric material 12.

The imaging suspension or ink 10 is coated over the tin oxide 9 on the transparent plate. The ink is of course the material from which the image is formed in the manner described earlier herein and in detail in the above referenced patents. The thickness of the layer of tin oxide 9 and especially the thickness of the ink 10 is greatly exaggerated in the drawings for illustrative purposes. The actual relative thickness of the ink is illustrated by noting that the position of the roller relative to the plate is such that if the ink is not present the outer surface of the roller contacts the plate. Therefore, when the ink is coated onto the transparent plate the roller and plate are separated by only a very small distance which is the thickness of the ink while compressed between the roller and plate.

The exposure mechanism includes the light source 13, the lens 14, and the transparency 15. The exposuremechanism is supported by the frame in the position shown in FIG. 1 and again the particular support structure is not shown in order to simplify the drawing to clarify the present discussion. The exposure mechanism is used to expose the ink to a light image thereby causing selective photosensitive particles within the ink to migrate between the electrodes (plate 4 and roller 3) to form the desired image. Normally, the

- desired image is a positive image formed from particles remaining at the plate after the particles are struck by light and driven away under the influence of the electric field from the plate to the roller.

The electric field required by the photoelectric process to cause the migration of the particles within the ink is established by the voltage source or battery 16 coupled at the negative terminal to the tin oxide layer 9 by the electrical conductor 17 and at second terminal to the center core 11 of roller 3 by the conductor 18.

It is of course necessary to close the switch 19 to apply the voltage potential across the electrodes. It is noted that the polarities of the voltages on the plate and roller may be reversed.

The carriage 2 is composed of the side walls 20 and 21 which are structurally tied to each other by the cross rods 22 and 23. The carriage is supported for movement along the rails 24 and 25 which are in turn rigidly supported by the frame 1. The carriage is slidably mounted on the rails by the sleeves 27 fixedly coupled ings (not shown) for assisting the sliding movement of the carriage along the rails. V v

The roller 3 is connected to shaft 28 which is journaled for rotation in the side walls 20 and 21 of the carriage by appropriate bearings. Also connected to shaft 28 is the roller sprocket 29 which along with the idler rollers 30 and 32 journaled in the side wall 20 and the chain 33 comprise the rotational drive mechanism 6. The chain is anchored to the frame at two ends by appropriate fasteners 34 and 35. The coil spring 37 connected in series with the chain near the anchor 34 is a bias for maintaining the tension in the chain and for preventing damage to the chain under excessive load conditions. The chain ispassed under the idler rollers 30 and 32 and over the teeth on the roller sprocket 29 to form the inverted U-shaped loop 38. The loop insures a positive engagement of the chain with the roller sprocket by virtue of the tension in the chain between the crest of the loop 39 and the idler rollers.

When the carriage moves along the rails, the chain is fed under the idler rollers and over the sprocket thereby increasing their positive engagement with the roller sprocket and causing the loop to move along the length of the chain with the carriage. As the loop moves from left to right, for example, the roller sprocket is rotated counterclockwise at an angular velocity directly related to the velocity of the carriage. Since the roller is coupled to the same shaft as the roller sprocket, it also rotates at the same angular velocity. The speed of the loop relative to the rails is substantially the same as the speed of the carriage. Consequently, the speed of a point at the pitch diameter of the sprocket is substantially the same as that of the carriage. By selecting the pitch diameter 40 of the sprocket and the outside diameter 42 of the roller to be substantially equal, the surface speed of the roller, i.e., the speed of the point on the periphery of the roller in contact with the plate 4, is made equal to and opposite in direction to the translational speed of the roller. This means that as the roller is passed over the ink on the plate the roller neither spins nor slides on the plate and therefore does not adversely affect an image formed on either the roller or the plate.

The chain is passed under the idler sprockets and over the top of the roller sprocket thereby causing the roller to rotate clockwise when it is moving from left to right and counterclockwise when moving from right to left. These are the appropriate rotational directions for the roller when the plate v4 is positioned above it. If the plate is positioned below the roller, the chain is looped over the bottom of the roller sprocket to obtain the proper rotation directions.

It is noted at this point that the rotational drive mechanism 6 is dependent for operation solely upon the movement of the roller and not the means forpropel ling the roller. Therefore the rotational drive mechanism 6 is capable of functioning whether the carriage is moved along the rails by hand or by a mechanical drive mechanism such as the translational drive mechanism 7'.

The translational drive mechanism 7 includes the conventional hydraulic double acting cylinder 43 and associated fluid flow control apparatus. The cylinder has the piston rod 45 coupled to the cross rod 23 on the the piston rod is extended and retracted. The extension and retraction of the piston rod is controlled by the hand operated three-position four way spool valve 47 represented schematically in FIG. 1. The valve is shown at its center position with the fluid from pump 48 being routed to the reservoir 49 thereby holding the piston rod stationary. To extend the piston rod the valve is switched to its left position thereby routing the fluid from the pump to the right end of the cylinder while the fluid on the other side of the cylinder piston is vented to the reservoir. To retract the piston rod the valve is switched to its right position and the fluid from the pump is routed to the left end of the cylinder while the fluid initially pumped to the other end of the cylinder is now vented to the reservoir.

If the plate 4 is supported on the frame 1 so as to move independently of the carriage in a direction opposite to the movement of the carriage, the actual translational speed of the roller is no longer the speed of the carriage but the sum of the carriage and the plate speeds. In this situation it is necessary to impart a surface speed to the roller that is greater than the carriage speed. This is accomplished by increasing the pitch diameter of the roller sprocket until the surface speed of the roller equals the relative speed between the roller and plate. Doing so prevents the roller from sliding across the plate. Similarly, if the plate 4 is supported by the frame 1 so as to move in the same direction as the carriage but at a slower speed it is necessary to make the pitch diameter of the sprocket less than the roller diameter to prevent the roller from spinning on the surface of the plate.

The presently preferred embodiment of the invention utilizes a link chain for the chain 30 but a timing belt and appropriate mating sprocket can be substituted therefore. It is also possible to use a friction belt in place of the chain if the friction engagement between the belt and roller sprocket or pulley in this case is sufficient to prevent slippage. In any case, the positive engagement of the sprocket or pulley with a mating flexible web-like member, whether a chain, belt, timing belt or equivalent device is insured by forming the U- shaped loop in the web-like member by passing it under idler sprockets and over the roller sprocket.

One advantage offered by the rotational drive mechanism utilizing the looped chain is that the chain need not be precisely aligned to the path followed by the carriage or to the roller sprocket because of the inherent flexibility of the chain (or other webbed member). This of course permits the tolerances for aligning the chain relative to the rails and sprocket to be relatively wide. As a result, the present rotational drive mechanism is extremely versatile and may be incorporated into many diverse machine structures. Another advantage of the present invention which increases its versatility is the fact that it is completely independent of the translational drive mechanism. However, the looped chain drive mechanism of the present invention may be used in a system where the carriage is propelled by a mechanism which develops its movement by engaging the chain 30 at some point near oraway from the loop.

What is claimed is:

1. In a photoelectrophoretic imaging machine of the typewherein images are formed from an imaging suspension exposed to a light image and subjected to electric field, said exposure being through at least one of two electrodes used to establish the electric field with at least one electrode being a roller, the improvement comprising a drive means for rotating a roller electrode at an angular velocity that substantially prevents spinning and slipping between said roller and the-other electrode including an immovable web-like member fixedly supported relative to said other electrode along a path defined by-the relative movement between the electrodes, means for engaging said web-like member and the roller to rotate the roller as the electrodes move relative to one another, said drive means including sprocket means coupled to said roller electrode for rotating the roller by engagement with a loop in said web-like member such that movement of the loop rotates the roller.

2. The machine of claim 1 wherein said roller electrode is journaled in a carriage supported for movement on rail means fixedly coupled to a frame in which said other electrode is fixedly coupled and wherein said drive means further includes first and second idler members coupled to said carriage on opposite sides of said sprocket means with the web-like member passing around said idler means and over said sprocket means to form said loop whereby movement of the carriage along the rail means causes movement of the loop along the web-like member and rotation of the roller.

3. The machine of claim 2 wherein said sprocket means includes a pitch diameter substantially equal to the diameter of said roller electrode to obtain a surface speed for a point on the periphery of the roller substantially equal and opposite to the translational speed of the roller. 

1. In a photoelectrophoretic imaging machine of the type wherein images are formed from an imaging suspension exposed to a light image and subjected to electric field, said exposure being through at least one of two electrodes used to establish the electric field with at least one electrode being a roller, the improvement comprising a drive means for rotating a roller electrode at an angular velocity that substantially prevents spinning and slipping between said roller and the other electrode including an immovable web-like member fixedly supported relative to said other electrode along a path defined by the relative movement between the electrodes, means for engaging said web-like member and the roller to rotate the roller as the electrodes move relative to one another, said drive means including sprocket means coupled to said roller electrode for rotating the roller by engagement with a loop in said web-like member such that movement of the loop rotates the roller.
 2. The machine of claim 1 wherein said roller electrode is journaled in a carriage supported for movement on rail means fixedly coupled to a frame in which said other electrode is fixedly coupled and wherein said drive means further includes first and second idler members coupled to said carriage on opposite sides of said sprocket means with the web-like member passing around said idler means and over said sprocket means to form said loop whereby movement of the carriaGe along the rail means causes movement of the loop along the web-like member and rotation of the roller.
 3. The machine of claim 2 wherein said sprocket means includes a pitch diameter substantially equal to the diameter of said roller electrode to obtain a surface speed for a point on the periphery of the roller substantially equal and opposite to the translational speed of the roller. 